draft: ruby to json

json_to_ruby.rs

use magnus::{
    class, define_class,
    encoding::{CType, RbEncoding},
    exception::runtime_error,
    function, method,
    prelude::*,
    scan_args::get_kwargs,
    value::Value,
    IntoValue, KwArgs, RArray, RHash, RObject, RString, Ruby,
};
use serde::{ser, Serialize};

/// Converts serde-compatible types to Ruby objects using instance variables.
pub struct RubyObjectSerializer<'rb, T> {
    ruby: &'rb Ruby,
    r: T,
}

#[derive(Debug)]
pub struct Error {}

impl ser::Error for Error {
    fn custom<T>(msg: T) -> Self
    where
        T: std::fmt::Display,
    {
        todo!()
    }
}

impl std::fmt::Display for Error {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "")
    }
}

impl std::error::Error for Error {}

type Result<T> = std::result::Result<T, Error>;

// By convention, the public API of a Serde serializer is one or more `to_abc`
// functions such as `to_string`, `to_bytes`, or `to_writer` depending on what
// Rust types the serializer is able to produce as output.
//
// This basic serializer supports only `to_string`.
pub fn to_ruby<T>(value: &T) -> Result<Value>
where
    T: Serialize,
{
    let ruby = match Ruby::get() {
        Ok(ruby) => ruby,
        Err(e) => return Err(Error {}),
    };
    let mut serializer = RubyObjectSerializer {
        ruby: &ruby,
        r: ruby.qnil().into_value(),
    };
    value.serialize(&mut serializer)
}

impl<'rb, T> ser::Serializer for &'rb mut RubyObjectSerializer<'rb, T>
where
    T: magnus::IntoValue,
{
    // The output type produced by this `Serializer` during successful
    // serialization. Most serializers that produce text or binary output should
    // set `Ok = ()` and serialize into an `io::Write` or buffer contained
    // within the `Serializer` instance, as happens here. Serializers that build
    // in-memory data structures may be simplified by using `Ok` to propagate
    // the data structure around.
    type Ok = Value;

    // The error type when some error occurs during serialization.
    type Error = Error;

    // Associated types for keeping track of additional state while serializing
    // compound data structures like sequences and maps. In this case no
    // additional state is required beyond what is already stored in the
    // Serializer struct.
    type SerializeSeq = &'rb mut RubyObjectSerializer<'rb, RArray>;
    type SerializeTuple = &'rb mut RubyObjectSerializer<'rb, RArray>;
    type SerializeTupleStruct = Self;
    type SerializeTupleVariant = Self;
    type SerializeMap = Self;
    type SerializeStruct = Self;
    type SerializeStructVariant = Self;

    // Here we go with the simple methods. The following 12 methods receive one
    // of the primitive types of the data model and map it to JSON by appending
    // into the output string.
    fn serialize_bool(self, v: bool) -> Result<Value> {
        Ok(if v {
            self.ruby.qtrue().into_value()
        } else {
            self.ruby.qfalse().into_value()
        })
    }

    fn serialize_i8(self, v: i8) -> Result<Value> {
        self.serialize_i64(v.into())
    }

    fn serialize_i16(self, v: i16) -> Result<Value> {
        self.serialize_i64(v.into())
    }

    fn serialize_i32(self, v: i32) -> Result<Value> {
        self.serialize_i64(v.into())
    }

    fn serialize_i64(self, v: i64) -> Result<Value> {
        Ok(self.ruby.integer_from_i64(v.into()).into_value())
    }

    fn serialize_u8(self, v: u8) -> Result<Value> {
        self.serialize_u64(v.into())
    }

    fn serialize_u16(self, v: u16) -> Result<Value> {
        self.serialize_u64(v.into())
    }

    fn serialize_u32(self, v: u32) -> Result<Value> {
        self.serialize_u64(v.into())
    }

    fn serialize_u64(self, v: u64) -> Result<Value> {
        Ok(self.ruby.integer_from_u64(v.into()).into_value())
    }

    fn serialize_f32(self, v: f32) -> Result<Value> {
        self.serialize_f64(v.into())
    }

    fn serialize_f64(self, v: f64) -> Result<Value> {
        match self.ruby.r_float_from_f64(v) {
            Ok(f) => Ok(f.into_value()),
            Err(f) => Ok(f.into_value()),
        }
    }

    // Serialize a char as a single-character string. Other formats may
    // represent this differently.
    fn serialize_char(self, v: char) -> Result<Value> {
        Ok(self.ruby.str_from_char(v).into_value())
    }

    // This only works for strings that don't require escape sequences but you
    // get the idea. For example it would emit invalid JSON if the input string
    // contains a '"' character.
    fn serialize_str(self, v: &str) -> Result<Value> {
        Ok(self.ruby.str_new(v).into_value())
    }

    // Serialize a byte array as an array of bytes. Could also use a base64
    // string here. Binary formats will typically represent byte arrays more
    // compactly.
    fn serialize_bytes(self, v: &[u8]) -> Result<Value> {
        Ok(self.ruby.str_from_slice(v).into_value())
    }

    // An absent optional is represented as the JSON `null`.
    fn serialize_none(self) -> Result<Value> {
        Ok(self.ruby.qnil().into_value())
    }

    // A present optional is represented as just the contained value. Note that
    // this is a lossy representation. For example the values `Some(())` and
    // `None` both serialize as just `null`. Unfortunately this is typically
    // what people expect when working with JSON. Other formats are encouraged
    // to behave more intelligently if possible.
    fn serialize_some<F>(self, value: &F) -> Result<Value>
    where
        F: ?Sized + Serialize,
    {
        value.serialize(self)
    }

    // In Serde, unit means an anonymous value containing no data. Map this to
    // JSON as `null`.
    fn serialize_unit(self) -> Result<Value> {
        self.serialize_none()
    }

    // Unit struct means a named value containing no data. Again, since there is
    // no data, map this to JSON as `null`. There is no need to serialize the
    // name in most formats.
    fn serialize_unit_struct(self, _name: &'static str) -> Result<Value> {
        self.serialize_unit()
    }

    // When serializing a unit variant (or any other kind of variant), formats
    // can choose whether to keep track of it by index or by name. Binary
    // formats typically use the index of the variant and human-readable formats
    // typically use the name.
    fn serialize_unit_variant(
        self,
        _name: &'static str,
        _variant_index: u32,
        _variant: &'static str,
    ) -> Result<Value> {
        self.serialize_unit()
    }

    // As is done here, serializers are encouraged to treat newtype structs as
    // insignificant wrappers around the data they contain.
    fn serialize_newtype_struct<NewType>(
        self,
        _name: &'static str,
        value: &NewType,
    ) -> Result<Value>
    where
        NewType: ?Sized + Serialize,
    {
        value.serialize(self)
    }

    // Note that newtype variant (and all of the other variant serialization
    // methods) refer exclusively to the "externally tagged" enum
    // representation.
    //
    // Serialize this to JSON in externally tagged form as `{ NAME: VALUE }`.
    fn serialize_newtype_variant<NewType>(
        self,
        _name: &'static str,
        _variant_index: u32,
        _variant: &'static str,
        value: &NewType,
    ) -> Result<Value>
    where
        NewType: ?Sized + Serialize,
    {
        value.serialize(&mut *self)
    }

    // Now we get to the serialization of compound types.
    //
    // The start of the sequence, each value, and the end are three separate
    // method calls. This one is responsible only for serializing the start,
    // which in JSON is `[`.
    //
    // The length of the sequence may or may not be known ahead of time. This
    // doesn't make a difference in JSON because the length is not represented
    // explicitly in the serialized form. Some serializers may only be able to
    // support sequences for which the length is known up front.
    fn serialize_seq(self, len: Option<usize>) -> Result<Self::SerializeSeq> {
        Ok(&mut RubyObjectSerializer {
            ruby: &self.ruby,
            r: self.ruby.ary_new_capa(len.unwrap_or(0)),
        })
    }

    // Tuples look just like sequences in JSON. Some formats may be able to
    // represent tuples more efficiently by omitting the length, since tuple
    // means that the corresponding `Deserialize implementation will know the
    // length without needing to look at the serialized data.
    fn serialize_tuple(self, len: usize) -> Result<Self::SerializeTuple> {
        Ok(&mut RubyObjectSerializer {
            ruby: &self.ruby,
            r: self.ruby.ary_new_capa(len),
        })
    }

    // Tuple structs look just like sequences in JSON.
    fn serialize_tuple_struct(
        self,
        _name: &'static str,
        len: usize,
    ) -> Result<Self::SerializeTupleStruct> {
        self.serialize_seq(Some(len));
        todo!()
    }

    // Tuple variants are represented in JSON as `{ NAME: [DATA...] }`. Again
    // this method is only responsible for the externally tagged representation.
    fn serialize_tuple_variant(
        self,
        _name: &'static str,
        _variant_index: u32,
        variant: &'static str,
        _len: usize,
    ) -> Result<Self::SerializeTupleVariant> {
        variant.serialize(&mut *self)?;
        todo!()
    }

    // Maps are represented in JSON as `{ K: V, K: V, ... }`.
    fn serialize_map(self, _len: Option<usize>) -> Result<Self::SerializeMap> {
        todo!()
    }

    // Structs look just like maps in JSON. In particular, JSON requires that we
    // serialize the field names of the struct. Other formats may be able to
    // omit the field names when serializing structs because the corresponding
    // Deserialize implementation is required to know what the keys are without
    // looking at the serialized data.
    fn serialize_struct(self, _name: &'static str, len: usize) -> Result<Self::SerializeStruct> {
        self.serialize_map(Some(len));
        todo!()
    }

    // Struct variants are represented in JSON as `{ NAME: { K: V, ... } }`.
    // This is the externally tagged representation.
    fn serialize_struct_variant(
        self,
        _name: &'static str,
        _variant_index: u32,
        variant: &'static str,
        _len: usize,
    ) -> Result<Self::SerializeStructVariant> {
        variant.serialize(&mut *self)?;
        todo!()
    }
}

// The following 7 impls deal with the serialization of compound types like
// sequences and maps. Serialization of such types is begun by a Serializer
// method and followed by zero or more calls to serialize individual elements of
// the compound type and one call to end the compound type.
//
// This impl is SerializeSeq so these methods are called after `serialize_seq`
// is called on the Serializer.
impl<'rb> ser::SerializeSeq for &'rb mut RubyObjectSerializer<'rb, RArray> {
    type Ok = Value;
    type Error = Error;

    // Serialize a single element of the sequence.
    fn serialize_element<T>(&mut self, value: &T) -> Result<()>
    where
        T: ?Sized + Serialize,
    {
        value.serialize(&mut **self);
        todo!()
    }

    // Close the sequence.
    fn end(self) -> Result<Value> {
        todo!()
    }
}

// Same thing but for tuples.
impl<'rb> ser::SerializeTuple for &'rb mut RubyObjectSerializer<'rb, RArray> {
    type Ok = Value;
    type Error = Error;

    fn serialize_element<T>(&mut self, value: &T) -> Result<()>
    where
        T: ?Sized + Serialize,
    {
        value.serialize(&mut **self);
        todo!()
    }

    fn end(self) -> Result<Value> {
        todo!()
    }
}

// Same thing but for tuple structs.
impl<'rb, T> ser::SerializeTupleStruct for &'rb mut RubyObjectSerializer<'rb, T>
where
    T: IntoValue,
{
    type Ok = Value;
    type Error = Error;

    fn serialize_field<F>(&mut self, value: &F) -> Result<()>
    where
        F: ?Sized + Serialize,
    {
        todo!()
    }

    fn end(self) -> Result<Value> {
        todo!()
    }
}

// Tuple variants are a little different. Refer back to the
// `serialize_tuple_variant` method above:
//
//    self.output += "{";
//    variant.serialize(&mut *self)?;
//    self.output += ":[";
//
// So the `end` method in this impl is responsible for closing both the `]` and
// the `}`.
impl<'rb, T> ser::SerializeTupleVariant for &'rb mut RubyObjectSerializer<'rb, T>
where
    T: IntoValue,
{
    type Ok = Value;
    type Error = Error;

    fn serialize_field<F>(&mut self, value: &F) -> Result<()>
    where
        F: ?Sized + Serialize,
    {
        todo!()
    }

    fn end(self) -> Result<Value> {
        todo!()
    }
}

// Some `Serialize` types are not able to hold a key and value in memory at the
// same time so `SerializeMap` implementations are required to support
// `serialize_key` and `serialize_value` individually.
//
// There is a third optional method on the `SerializeMap` trait. The
// `serialize_entry` method allows serializers to optimize for the case where
// key and value are both available simultaneously. In JSON it doesn't make a
// difference so the default behavior for `serialize_entry` is fine.
impl<'rb, T> ser::SerializeMap for &'rb mut RubyObjectSerializer<'rb, T>
where
    T: IntoValue,
{
    type Ok = Value;
    type Error = Error;

    // The Serde data model allows map keys to be any serializable type. JSON
    // only allows string keys so the implementation below will produce invalid
    // JSON if the key serializes as something other than a string.
    //
    // A real JSON serializer would need to validate that map keys are strings.
    // This can be done by using a different Serializer to serialize the key
    // (instead of `&mut **self`) and having that other serializer only
    // implement `serialize_str` and return an error on any other data type.
    fn serialize_key<F>(&mut self, key: &F) -> Result<()>
    where
        F: ?Sized + Serialize,
    {
        todo!()
    }

    fn serialize_value<F>(&mut self, value: &F) -> Result<()>
    where
        F: ?Sized + Serialize,
    {
        todo!()
    }

    fn end(self) -> Result<Value> {
        todo!()
    }
}

// Structs are like maps in which the keys are constrained to be compile-time
// constant strings.
impl<'rb, T> ser::SerializeStruct for &'rb mut RubyObjectSerializer<'rb, T>
where
    T: magnus::IntoValue,
{
    type Ok = Value;
    type Error = Error;

    fn serialize_field<F>(&mut self, key: &'static str, value: &F) -> Result<()>
    where
        F: ?Sized + Serialize,
    {
        todo!()
    }

    fn end(self) -> Result<Value> {
        todo!()
    }
}

// Similar to `SerializeTupleVariant`, here the `end` method is responsible for
// closing both of the curly braces opened by `serialize_struct_variant`.
impl<'rb, T> ser::SerializeStructVariant for &'rb mut RubyObjectSerializer<'rb, T>
where
    T: magnus::IntoValue,
{
    type Ok = Value;
    type Error = Error;

    fn serialize_field<F>(&mut self, key: &'static str, value: &F) -> Result<()>
    where
        F: ?Sized + Serialize,
    {
        todo!()
    }

    fn end(self) -> Result<Value> {
        todo!()
    }
}

ruby_to_json.rs

fn ruby_to_json(
    any: Value,
    field_pos: Vec<String>,
) -> std::result::Result<serde_json::Value, Vec<SerializationError>> {
    use magnus::r_hash::ForEach;

    if let Some(any) = RHash::from_value(any) {
        let mut errs = vec![];
        let mut map = serde_json::Map::new();
        if any
            .foreach(|k: Value, v: Value| {
                let Some(k) = RString::from_value(k) else {
                    errs.push(SerializationError {
                        position: field_pos.clone(),
                        message: format!(
                            "expected every key in this hash to be string, but found key {:#}",
                            k
                        ),
                    });
                    return Ok(ForEach::Continue);
                };
                let Ok(k) = k.to_string() else {
                    errs.push(SerializationError {
                        position: field_pos.clone(),
                        message: format!(
                            "failed to convert key in this hash to be UTF-8 string: {:#}",
                            k
                        ),
                    });
                    return Ok(ForEach::Continue);
                };

                let mut field_pos = field_pos.clone();
                field_pos.push(k.clone());

                match ruby_to_json(v, field_pos) {
                    Ok(json_value) => {
                        map.insert(k.to_string(), json_value);
                    }
                    Err(e) => errs.extend(e),
                }
                Ok(ForEach::Continue)
            })
            .is_err()
        {
            errs.push(SerializationError {
                position: field_pos.clone(),
                message: "failed to iterate over hash".to_string(),
            });
        };

        if !errs.is_empty() {
            return Err(errs);
        }

        return Ok(serde_json::Value::Object(map));
    }

    if let Some(any) = RArray::from_value(any) {
        let mut errs = vec![];
        let mut arr = vec![];

        for (i, value) in any.each().enumerate() {
            let mut field_pos = field_pos.clone();
            field_pos.push(i.to_string());
            let Ok(value) = value else {
                errs.push(SerializationError {
                    position: field_pos.clone(),
                    message: format!("failed to enumerate array element at index {}", i),
                });
                continue;
            };
            match ruby_to_json(value, field_pos) {
                Ok(json_value) => {
                    arr.push(json_value);
                }
                Err(e) => errs.extend(e),
            }
        }

        if !errs.is_empty() {
            return Err(errs);
        }

        return Ok(serde_json::Value::Array(arr));
    }

    if let Some(any) = magnus::Integer::from_value(any) {
        if let Ok(any) = any.to_i64() {
            return Ok(serde_json::Value::Number(serde_json::Number::from(any)));
        }
        if let Ok(any) = any.to_u64() {
            return Ok(serde_json::Value::Number(serde_json::Number::from(any)));
        }

        return Err(vec![SerializationError {
            position: field_pos,
            message: "failed to convert integer to i64 or u64".to_string(),
        }]);
    }

    if let Some(any) = magnus::Float::from_value(any) {
        let Some(as_json) = serde_json::Number::from_f64(any.to_f64()) else {
            return Err(vec![SerializationError {
                position: field_pos,
                message: format!("cannot convert {:#} to float", any),
            }]);
        };
        return Ok(serde_json::Value::Number(as_json));
    }

    //if let Some(any) = RString::from_value(ruby) {
    //    match any.to_string() {}
    //    return Ok(serde_json::Value::String(any.to_string()));
    //}

    Err(vec![SerializationError {
        position: field_pos,
        message: "the rest of the cases are unsupported".to_string(),
    }])
}